The present invention relates to an eye refractive power measuring apparatus for measuring eye refractive power such as a spherical refractive power, an astigmatic power, and an astigmatism angle of a subject's eye, and a calibration method of an eye refractive power measuring apparatus.
As a method for measuring eye refractive power power for refracting light) of a subject's eye, a method has been known in which a target beam used for measurement is projected onto a fundus of the subject's eye, and an eye refractive power is measured based on the size, etc. of an image formed when light reflected on the fundus is imaged. Furthermore, an eye refractive power measuring apparatus that measures eye refractive power automatically based on this method (automatic refractometer has been known.
In such eye refractive power measuring apparatus, an eye refractive power measuring apparatus is known which, for the purpose of improving measurement accuracy of eye refractive power, includes a mechanism for moving a lens or a light receiving element. For example, in an eye refractive power measuring apparatus according to Japanese Patent Application Publication No. 2005-185523 (hereinafter, Patent Document 1), by moving a lens, etc. by a moving mechanism in accordance with an eye refractive power of a subject's eye, a target beam projected onto a fundus is focused. Therefore, it is possible to reduce measurement errors due to defocusing of the target beam.
In the eye refractive power measuring apparatus of Patent Document 1, in order to reduce the measurement errors in the eye refractive power, it is desirable that the lens, etc. is moved so that an optical axis of the lens matches an optical axis of an optical system. However, keeping the matching of the optical axes upon moving is difficult. There has been a problem that lowering of measurement accuracy due to misalignment of the optical axes is likely to occur.
To address the above problem, instead of providing a moving mechanism for moving the lens, etc. as described above, an eye refractive power measuring apparatus with a reduced movable mechanical portion is known in which a variable focus lens made of transparent silicone rubber or the like is arranged at a position conjugate with a pupil. For example, in the eye refractive power measuring apparatus of Japanese Patent Application Publication No. 63-031633 (hereinafter, Patent Document 2), in a state in which the position of the lens, etc. is fixed, the target beam projected onto the fundus is focused by moving a focal position of the lens, etc. Therefore, misalignment of the optical axes by the movement of the lens, etc. as above can be suppressed. Deterioration of measurement accuracy can be thus suppressed. Further, because a moving mechanism for moving the lens, etc. is not required, a configuration of the apparatus can be simplified. The apparatus itself can be downsized.